A: 收集H2
B: O2验满
C: 配制20%的Ca(OH)2溶液
D:除去CO中的CO2
-15的相反数是____ .
起重机吊着重1000N的物体,当物体在空中静止时:
——Millie,is there anything else you want to know about Yangzhou paper cutting?——Yes,I am still wondering __________ .